Free weights, dumbbells, barbells... all great tools. But a weight machine has advantages that they just can't match.

They're much safer. True, you have to exercise caution when you use one. But the odds of dropping a weight at the wrong angle are eliminated and spotting someone on a machine is much, much easier.

They're simple to use, yet provide a wide range of exercises to work every muscle group. Almost all provide some means of working those triceps and deltoids, almost as many have a station to work biceps, too. But a good weight machine will offer mechanisms to work the hamstrings and quadriceps, all back muscle groups and more with one easy method.

Stack machines, for example, provide a stack of weights that is adjustable simply by moving a pin. Plate loads offer the same basic option, but the weights are removable. Safe, quick and practically indestructible you can move the weight from 10 lbs to 100 lbs or more with one quick movement. No need to waste time and energy removing a friction lever or bolt, strapping on several discs as you do with free weights.

An all purpose weight machine will offer a sturdy set of 'handlebars' for working the trapezoids, deltoids, pecs and other groups. It will include a similar bar on a cable to work abs, biceps, triceps and more. The dorsal muscles get a work out from some that offer a swivel and plate assembly attached to the weights. Adjustable with ease. Don't forget about those built-in chinning bars, either. Try to do pull-ups with a set of barbells.

Some even incorporate a rowing machine to get one of the best full body workouts you can imagine. They work every muscle in your body in one way or another and also are great for the cardiovascular system.

A good one will also have an adjustable incline on the bench that offers a safe, easy way to do sit-ups and crunches at varying levels. That same bench makes it a snap to do bench presses using a range of weights. You'll never outgrow a good weight machine. It lets you start at your level and keeps up with you as you rise in strength.

Some models allow the bench to double as an incline plane, which is great for those hyperextension exercises. That offers an excellent way to build abs, back muscles and more.

There are some potential drawbacks to weight machines, though.

They're much more expensive than free weights, so they should be looked as a long term investment. A basic set of dumbbells can run as little as $100. Most weight machines start at about $400 for anything that has more than the bare minimum and they go up from there.

From a workout perspective, it takes a good machine a little bit of planning to avoid overworking the same muscles in the same way. Because of their limited range of motion, it's possible to get stuck in a rut. Also, it simply takes more balance, coordination and strength in different directions to lift and balance, say, a 100 lb barbell than the same weight on a machine.

But a machine with lots of variation makes it possible to overcome all those potential problems without difficulty.